1. Field of the Invention
This invention relates to helicopters in general, and more particularly to a helicopter of the type having two coaxial counterrotating rotors with a drive mechanism interposed between the normal power plant of the aircraft and the rotors.
2. Description of the Prior Art
In general there are known two main types of helicopters: (1) the type having two counterrotating rotors (which may or may not be coaxial), and (2) the type having a single main rotor and an auxiliary anti-torque tail rotor.
In the case of helicopters pertaining to type (2) the auxiliary anti-torque tail rotor requires about 20 to 30% of the power which the power plant is capable of delivering, this power being subtracted from the power which otherwise would be deliverable to the main rotors, contrarily to the case of helicopters having two counterrotating rotors in which the torque of one rotor acts in a direction opposite to the direction of the torque of the other rotor. Stated in another way, the power-weight ratio is more favorable in helicopters pertaining to type (1). Also, in the case of helicopters pertaining to type (2) the drive means provided between the power plant and the tail rotor makes more complicated the design and construction and increase the weight of the aircraft, thus worsening even more the power-weight ratio. Another fact is that the main rotor works asymmetrically because the lift generated by the blade of the main rotor which is rotating against the relative wind produced by the horizontal displacement of the aircraft is greater than that produced by the other blade, thus producing a tendency to lateral unbalance which is cyclically reverted at each half-revolution of the rotor. Such a lateral instability must be corrected by rather complicated mechanisms which change proportionately and oppositely the angle of attack of each blade with respect to the other at each half-revolution of the rotor.
A helicopter pertaining to type (1) allows the elimination of the above mentioned drawbacks. It does not require the use of an antitorque tail rotor since the oppositely rotating rotors produce corresponding torques of opposite directions mutually cancelling one another. The absence of an anti-torque tail rotor allows a maximum utilization of the power generated by the power plant. Also, the elimination of the tail rotor allows a simplification of the drive and control mechanism thereof, thus reducing the weight of the aircraft and improving the power-weight ratio. Referring to the asymmetry of lift produced by the relative wind, which is characteristic of each rotor individually considered, it must be remembered that since the rotors are coaxial and rotate in opposite directions, said asymmetry in one rotor is opposite to the asymmetry in the other, and thus are mutually cancelled. At least theoretically, this allows greater simplicity and better lateral balance.
Bearing in mind these favorable characteristics of the helicopter having two coaxial counterrotating rotors, it would have been only logical to expect that this type of helicopter would have gained a considerably greater acceptance than the single rotor helicopter having a tail rotor. However, just the contrary has happened. This apparently strange fact is due to a series of factors which detract from a good performance of the helicopter with two coaxial counterrotating rotors. Some of the factors involved are: the efficiencies of the rotors are unequal, the cause of which is the influence of the upper rotor air stream on the lower rotor, and the different aerodynamic conditions of the corresponding horizontal air layers in which each rotor is working. This is constantly producing deviations from the normal flight attitude and normal flight path. This is turn requires that the pilot makes constantly corrections by means of the flight controls of the aircraft and this makes pilotage a very tiresome task for the air pilot, specially during long flights, and a dangerous task during certain maneuvers such as aerial spraying with plaguicide and herbicide compounds and the like at low altitude, rescue operations, etc., in which high stability is an essential security factor.
It is known that pilot fatigue is the main factor producing serious or fatal accidents.
Thus in the light of all what has been said above, it would be highly desirable to improve the flight stability and maneuverability of helicopters of the type having two coaxial counterrotating rotors and thus reducing pilot fatigue.
It will also be obvious to the skilled in this art, that the continuously variable instabilities and asymmetries of the working conditions of the rotors produce continuously variable power demands from each rotor and thus produce continuously increasing and decreasing stresses and strains in the component parts and the materials from which they are made, inducing vibrations which reduce the useful life thereof and there being the potential risk of fractures of critical components. Thus eliminating such instabilities and asymmetries it would be possible to extend the useful life of such component parts obtaining the same security factor with lesser amount of material and/or lesser critical quality thereof with the possibility of increasing the power-weight ratio and highly increasing the security factor.
To achieve such desideratums it would be necessary that each rotor individually obtains in each instant the necessary proportion of the total motive power which the power plant is capable of producing and that this distribution of power would be as exact as possible. In other words, if in a certain instant one of the rotors requires 5% more power than the other one and the total power supplied by the power plant is 100%, then said rotor would be supplied with 55% of the total available power and the other rotor would be supplied with only 45%. Moreover, this distribution must take place automatically without any operation of the controls of the aircraft by the pilot. This would reduce considerably pilot fatigue and the stresses imposed on critical component parts.